Rechargeable Molten Salt Battery Freezes Energy In Place For Long-Term Storage

An anonymous reader quotes a report from Scientific American: During spring in the Pacific Northwest, meltwater from thawing snow rushes down rivers and the wind often blows hard. These forces spin the region's many power turbines and generate a bounty of electricity at a time of mild temperatures and relatively low energy demand. But much of this seasonal surplus electricity -- which could power air conditioners come summer -- is lost because batteries cannot store it long enough. Researchers at Pacific Northwest National Laboratory (PNNL), a Department of Energy national laboratory in Richland, Wash., are developing a battery that might solve this problem. In a recent paper published in Cell Reports Physical Science, they demonstrated how freezing and thawing a molten salt solution creates a rechargeable battery that can store energy cheaply and efficiently for weeks or months at a time.

Most conventional batteries store energy as chemical reactions waiting to happen. When the battery is connected to an external circuit, electrons travel from one side of the battery to the other through that circuit, generating electricity. To compensate for the change, charged particles called ions move through the fluid, paste or solid material that separates the two sides of the battery. But even when the battery is not in use, the ions gradually diffuse across this material, which is called the electrolyte. As that happens over weeks or months, the battery loses energy. Some rechargeable batteries can lose almost a third of their stored charge in a single month.

'In our battery, we really tried to stop this condition of self-discharge,' says PNNL researcher Guosheng Li, who led the project. The electrolyte is made of a salt solution that is solid at ambient temperatures but becomes liquid when heated to 180 degrees Celsius -- about the temperature at which cookies are baked. When the electrolyte is solid, the ions are locked in place, preventing self-discharge. Only when the electrolyte liquifies can the ions flow through the battery, allowing it to charge or discharge. Creating a battery that can withstand repeated cycles of heating and cooling is no small feat. Temperature fluctuations cause the battery to expand and contract, and the researchers had to identify resilient materials that could tolerate these changes. The result is a rechargeable battery made from relatively inexpensive materials that can store energy for extended periods. 'Right now the experimental technology is aimed at utility-scale and industrial uses,' notes the report. 'The PNNL team plans to continue developing the technology, but ultimately it will be up to industry to develop a commercial product.'

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